An image capturing apparatus performs focus detection based on a pair of image signals obtained from an image sensor including pixels each having a pair of photoelectric conversion units capable of outputting the pair of image signals obtained by independently receiving a pair of light beams that have passed through different exit pupil regions of an imaging optical system. In the focus detection, an f-number of the imaging optical system is acquired, the pair of image signals undergo filtering using a first filter formed from an summation filter when the f-number is less than a predetermined threshold, or using a second filter formed from the summation filter and a differential filter when the f-number is not less than the threshold, and focus detection is performed by a phase difference method based on the pair of filtered image signals.